66 



TROPICAL CLIMATOLOGY 



their own cultivation; and so densely are they placed that a failure to produce 

 their own crops results in a most severe famine, which can only be coped with 

 by the most energetic action of the Government. 



2. North- West and South-East Monsoons. — These are to be found in the 

 Southern Hemisphere, and are depicted in Fig. 6 in the region of Australia. 



3. West Monsoon. — Dove described as the west monsoon of the line a 

 wind which blows in a south-westerly direction along the coast of Africa 

 from Cape Verde down to Walfisch Bay. These winds, however, are variable, 

 and in the Gulf of Guinea are interrupted very often by calms. 



Some people describe the winds along the eastern and western coasts of 

 South America as monsoons, but they hardly come under this term. 



In typical monsoon regions the rains follow the vertical sun, and the type 

 of temperature is the so-called tropical type, with one maximum and one 

 minimum. 



It must be admitted that this simple classification, like all classifications, 

 fails to explain everything, and there are numerous exceptions showing com- 

 binations of equatorial, trade-wind, and monsoon types. 



IV. Mountain Climates. — ^We have already pointed out the effect 

 of altitude in lowering the temperature, and, indeed, Herschel, 

 many years ago, showed that for every 300 feet of increase in 

 altitude there was a decrease of 1° F. in temperature, and for every 

 180 metres a decrease of 1° C. These statements are only partially 

 correct, for the temperature at a given altitude depends upon the 

 expansion and humidity of the air, the clearness of the atmosphere, 

 together with the quantity of earth at the given locality, and the 

 nature of the wind blowing at the time of the observations. Perhaps 

 of all these the most important is the expansion of the air, for, as is 

 well known, it expands when heated- — i.e., the energy represented 

 by heat is converted into motion, and hence the temperature falls. 

 This will in part be counteracted by the heat produced by the 

 condensation of aqueous vapour, even at high altitudes, and upon 

 this condensation and cloud-formation will depend how much 

 of the heat, radiating from the earth into the air, is retained. The 

 lessened amount of earth in high altitudes is also a factor, as there 

 is less earth to retain heat, and hence less heat is given off into the 

 air. It is obvious that movements of the air— the winds— must 

 have a great effect, depending upon their origin from warm or cold 

 sources. Hence, though in general the rule mentioned above as to 

 a relationship between temperature and altitude holds good, it is 

 only approximate, as the connection between the two is complex, 

 not simple. 



In the tropics, therefore, the low country possesses the true 

 tropical climate, while the climatological conditions of the hills are 

 quite different. Indeed, as Ward has said, the climates of many 

 tropical plateaus and mountains have the reputation of having a 

 perpetual spring, but though that may be so at certain latitudes, 

 if considerable elevations are reached a peipetual winter exists, 

 with snow all the year round, even on the Equator. 



The great blessing of these elevations in the tropics is that they 

 provide cool hill stations to which the resident of the plains may 

 resort during the hottest months, and in which sanatoria may be built 

 for the treatment of persons convalescent from lowland complaints. 



